Thyroid hormones are important in normal development and in maintaining metabolic homeostasis. For example, thyroid hormones stimulate the metabolism of cholesterol to bile acids and enhance the lipolytic responses of fat cells to other hormones.
Thyroid hormones also affect cardiac function both directly and indirectly, e.g., by increasing the metabolic rate. For example, tachycardia, increased stroke volume, increased cardiac index, cardiac hypertrophy, decreased peripheral vascular resistance and increased pulse pressure are observed in patients with hyperthyroidism.
Disorders of the thyroid gland are generally treated by administering either naturally occurring thyroid hormones or analogues that mimic the effects of thyroid hormones. Such analogues are called thyromimetics or thyroid receptor ligands.
Two naturally occurring thyroid hormones, 3,5,3′,5′-tetraiodo-L-thyronine (also referred to as “T4” or thyroxine) and 3,5,3′-triiodo-L-thyronine (also referred to as “T3”), are shown below:
T3 is more biologically active than T4, and differs from T4 by the absence of the 5′ iodine. T3 may be produced directly in the thyroid gland, or in peripheral tissues, by the removal of the 5′ iodine of T4 by deiodinase enzymes. Thyroid receptor ligands can be designed to be structurally similar to T3. In addition, naturally occurring metabolites of T3 are known.
As discussed above, thyroid hormones affect cardiac functioning, for example, by causing an increase in heart rate, and accordingly, an increase in oxygen consumption. While the increase in oxygen consumption can result in certain desired metabolic effects, nonetheless, it does place an extra burden on the heart, which in some situations, may give rise to damaging side effects. Therefore, as described in A. H. Underwood et al., Nature, 324: 425–429 (1986), efforts have been made to synthesize thyroid hormone analogs that function to lower lipids and serum cholesterol, without generating the adverse cardiac effects referred to above.
U.S. Pat. Nos. 4,766,121; 4,826,876; 4,910,305; and 5,061,798 disclose thyroid hormone mimetics, namely, 3,5-dibromo-3′-[6-oxo-3(1H)-pyridazinylmethyl]-thyronines.
U.S. Pat. No. 5,284,971 discloses thyromimetic cholesterol lowering agents, namely, 4-(3-cyclohexyl-4-hydroxy or -methoxy phenylsulfonyl)-3,5 dibromo-phenylacetic acid compounds.
U.S. Pat. Nos. 5,401,772 (also published European Patent Application 0 580 550); 5,654,468 and 5,569,674 disclose certain lipid lowering agents, namely, heteroacetic acid derivatives, more specifically oxamic acid derivatives, which compete with radiolabeled T3 in binding assays using rat liver nuclei and plasma membrane preparations.
Certain oxamic acids and derivatives thereof are known in the art, e.g., U.S. Pat. No. 4,069,343 describes the use of certain oxamic acids to prevent immediate type hypersensitivity reactions; U.S. Pat. No. 4,554,290 describes the use of certain oxamic acids to control pests on animals and plants; and U.S. Pat. No. 5,232,947 describes the use of certain oxamic acids to improve damaged cerebral functions of the brain.
In addition, certain oxamic acid derivatives of thyroid hormones are known in the art. For example, N. Yokoyama et al. in an article published in the Journal of Medicinal Chemistry, 38 (4): 695–707 (1995) describe replacing a —CH2 group in a naturally occurring metabolite of T3 with an —NH group resulting in —HNCOCO2H. Likewise, R. E. Steele et al. in an article published in International Congressional Service (Atherosclerosis X) 106: 321–324 (1995) and Z. F. Stephan et al. in an article published in Atherosclerosis, 126: 53–63 (1996), describe a certain oxamic acid derivative useful as a lipid-lowering thyromimetic agent that has reduced adverse cardiac activities.
Commonly assigned International Patent Application Publication No. WO 00/51971, published 8 Sep. 2000, and commonly assigned published European Patent Application EP 1 033 364, published 6 Sep. 2000, disclose certain oxamic acids and derivatives thereof as thyroid receptor ligands. Commonly assigned U.S. nonprovisional patent application, Ser. No. 09/671,668, filed 27 Sep. 1999, discloses certain 6-azauracil derivatives as thyroid receptor ligands. Commonly assigned U.S. provisional patent application, Ser. No. 60/177,987, filed 25 Jan. 2000, discloses certain tetrazole compounds as thyroid receptor ligands.
D. M. T. Chan et al., Tetrahedron Letters, 39: 2933–2936 (1998) discloses new N— and O-arylations with phenylboronic acids and cupric acetate.
International Patent Application Publication No. WO 00/58279, published 5 Oct. 2000, discloses diaryl derivatives and their use as medicaments.
International Patent Application Publication No. WO 00/07972, published 17 Feb. 2000, discloses glucocorticoid and thyroid hormone receptor ligands for the treatment of metabolic disorders.
International Patent Application Publication No. WO 00/39077, published 6 Jul. 2000, discloses novel thyroid receptor ligands.
A. H. Taylor et al., “Beneficial Effects of a Novel Thyromimetic on Lipoprotein Metabolism,” Molecular Pharmacology, 52:542–547 (1997), discloses beneficial effects of a novel thyromimetic on lipoprotein metabolism.
J. L. Stanton et al., “Synthesis and Biological Activity of Phenoxyphenyl Oxamic Acid Derivatives Related to L-Thyronine,” Bioorganic & Medicinal Chemistry Letters, 10: 1661–1663 (2000), discloses the synthesis and biological activity of phenoxyphenyl oxamic acid derivatives related to L-thyronine.
International Patent Application Publication No. WO 00/72810, published 7 Dec. 2000, discloses a method of treating hair loss using certain sulfonyl thyromimetic compounds. International Patent Application Publication No. WO 00/72811, published 7 Dec. 2000, discloses methods of treating hair loss using certain compounds described therein. International Patent Application Publication No. WO 00/72812, published 7 Dec. 2000, discloses methods of treating hair loss using certain diphenylether derivatives. International Patent Application Publication No. WO 00/72813, published 7 Dec. 2000, discloses methods of treating hair loss using certain diphenylmethane derivatives. International Patent Application Publication No. WO 00/72920, published 7 Dec. 2000, discloses certain substituted biaryl ether compounds and compositions for treating hair loss. International Patent Application Publication No. WO 00/73292, published 7 Dec. 2000, discloses certain biaryl compounds and compositions for treating hair loss.
Obesity is a major health risk that leads to increased mortality and incidence of Type 2 diabetes mellitus, hypertension and dyslipidemia. In the US, more than 50% of the adult population is overweight, and almost ¼ of the population is considered to be obese (BMI greater than or equal to 30). The incidence of obesity is increasing in the U.S. at a 3% cumulative annual growth rate. While the vast majority of obesity occurs in the US and Europe, the prevalence of obesity is also increasing in Japan. The prevalence of obesity in adults is 10%–25% in most countries of western Europe.
Obesity is a devastating disease. In addition to harming physical health, obesity can wreak havoc on mental health because obesity affects self-esteem, which ultimately can affect a person's ability to interact socially with others. Unfortunately, obesity is not well understood, and societal stereotypes and presumptions regarding obesity only tend to exacerbate the psychological effects of the disease. Because of the impact of obesity on individuals and society, much effort has been expended to find ways to treat obesity, but little success has been achieved in the long-term treatment and/or prevention of obesity. The present invention provides methods of treating obesity by administering to an obese patient or a patient at risk of becoming obese a therapeutically effective amount of a thyromimetic of the present invention.
The thyromimetics of the present invention can also be used to treat diabetes, atherosclerosis, hypertension, coronary heart disease, hypercholesterolemia, hyperlipidemia, thyroid disease, thyroid cancer, hypothyroidism, depression, glaucoma, cardiac arrhythmias, congestive heart failure, and osteoporosis.
In spite of the early discovery of insulin and its subsequent widespread use in the treatment of diabetes, and the later discovery of and use of sulfonylureas, biguanides and thiazolidenediones, such as troglitazone, rosiglitazone or pioglitazone, as oral hypoglycemic agents, the treatment of diabetes remains less than satisfactory.
The use of insulin currently requires multiple daily doses, usually by self-injection. Determination of the proper dosage of insulin requires frequent estimations of the sugar in urine or blood. The administration of an excess dose of insulin causes hypoglycemia, with effects ranging from mild abnormalities in blood glucose to coma, or even death. Treatment of non-insulin dependent diabetes mellitus (Type II diabetes, NIDDM) usually consists of a combination of diet, exercise, oral hypoglycemic agents, e.g., thiazolidenediones, and, in more severe cases, insulin. However, the clinically available hypoglycemic agents can have side effects that limit their use, or an agent may not be effective with a particular patient. In the case of insulin dependent diabetes mellitus (Type I), insulin is usually the primary course of therapy. Hypoglycemic agents that have fewer side effects or succeed where others fail are needed.
Atherosclerosis, a disease of the arteries, is recognized to be a leading cause of death in the United States and Western Europe. The pathological sequence leading to atherosclerosis and occlusive heart disease is well known. The earliest stage in this sequence is the formation of “fatty streaks” in the carotid, coronary and cerebral arteries and in the aorta. These lesions are yellow in color due to the presence of lipid deposits found principally within smooth-muscle cells and in macrophages of the intima layer of the arteries and aorta. Further, it is postulated that most of the cholesterol found within the fatty streaks, in turn, give rise to development of “fibrous plaques,” which consist of accumulated intimal smooth muscle cells laden with lipid and are surrounded by extra-cellular lipid, collagen, elastin and proteoglycans. The cells plus matrix form a fibrous cap that covers a deeper deposit of cell debris and more extra-cellular lipid. The lipid is primarily free and esterified cholesterol. A fibrous plaque forms slowly, and is likely in time to become calcified and necrotic, advancing to a “complicated lesion,” which accounts for arterial occlusion and tendency toward mural thrombosis and arterial muscle spasm that characterize advanced atherosclerosis.
Epidemiological evidence has firmly established hyperlipidemia as a primary risk factor in causing cardiovascular disease (CVD) due to atherosclerosis. In recent years, leaders of the medical profession have placed renewed emphasis on lowering plasma cholesterol levels, and low density lipoprotein cholesterol in particular, as an essential step in prevention of CVD. The upper limits of “normal” are now known to be significantly lower than heretofore appreciated. As a result, large segments of Western populations are now realized to be at particularly high risk. Such independent risk factors include glucose intolerance, left ventricular hypertrophy, hypertension, and being of the male sex. Cardiovascular disease is especially prevalent among diabetic subjects, at least in part because of the existence of multiple independent risk factors in this population. Successful treatment of hyperlipidemia in the general population, and in diabetic subjects in particular, is therefore of exceptional medical importance.
Hypertension (or high blood pressure) is a condition that occurs in the human population as a secondary symptom to various other disorders such as renal artery stenosis, pheochromocytoma or endocrine disorders. However, hypertension is also evidenced in many patients in whom the causative agent or disorder is unknown. While such “essential” hypertension is often associated with disorders such as obesity, diabetes and hypertriglyceridemia, the relationship between these disorders has not been elucidated. Additionally, many patients display the symptoms of high blood pressure in the complete absence of any other signs of disease or disorder.
It is known that hypertension can directly lead to heart failure, renal failure and stroke (brain hemorrhaging). These conditions are capable of causing death in a patient. Hypertension can also contribute to the development of atherosclerosis and coronary disease. These conditions gradually weaken a patient and can lead to death.
The exact cause of essential hypertension is unknown, though a number of factors are believed to contribute to the onset of the disease. Among such factors are stress, uncontrolled emotions, unregulated hormone release (the renin, angiotensin, aldosterone system), excessive salt and water due to kidney malfunction, wall thickening and hypertrophy of the vasculature resulting in constricted blood vessels and genetic factors.
The treatment of essential hypertension has been undertaken bearing the foregoing factors in mind. Thus, a broad range of beta-blockers, vasoconstrictors, angiotensin converting enzyme inhibitors and the like have been developed and marketed as antihypertensives. The treatment of hypertension utilizing these compounds has proven beneficial in the prevention of short-interval deaths such as heart failure, renal failure and brain hemorrhaging.
Hypertension has been associated with elevated blood insulin levels, a condition known as hyperinsulinemia. Insulin, a peptide hormone whose primary actions are to promote glucose utilization, protein synthesis and the formation and storage of neutral lipids, also acts to promote vascular cell growth and increase renal sodium retention, among other things. These latter functions can be accomplished without affecting glucose levels and are known causes of hypertension. Peripheral vasculature growth, for example, can cause constriction of peripheral capillaries while sodium retention increases blood volume. Thus, the lowering of insulin levels in hyperinsulinemics can prevent abnormal vascular growth and renal sodium retention caused by high insulin levels and thereby alleviate hypertension.
Hair loss is a common problem, which occurs, for example, through natural processes or is often chemically promoted through the use of certain therapeutic drugs designed to alleviate conditions such as cancer. Often such hair loss is accompanied by lack of hair regrowth which causes partial or full baldness.
As is well known in the art, hair growth occurs by a cycle of activity which involves alternating periods of growth and rest. This cycle is often divided into three main stages which are known as anagen, catagen and telogen. Anagen is the growth phase of the cycle and may be characterized by penetration of the hair follicle deep into the dermis with rapid proliferation of cells, which are differentiating to form hair. The next phase is catagen, which is a transitional stage marked by the cessation of cell division, and during which the hair follicle regresses through the dermis and hair growth is ceased. The next phase, telogen, is often characterized as the resting stage during which the regressed follicle obtains a germ with tightly packed dermal papilla cells. At telogen, the initiation of a new anagen phase is caused by rapid cell proliferation in the gern, expansion of the dermal papilla, and elaboration of basement membrane components. When hair growth ceases, most of the hair follicles reside in telogen and anagen is not engaged, thus causing the onset of full or partial baldness.
Interestingly, it is known that the thyroid hormone known as thyroxine (“T4”) converts to thyronine (“T3”) in human skin by deiodinase I, a selenoprotein. Selenium deficiency causes a decrease in T3 levels due to a decrease in deiodinase I activity; this reduction in T3 levels is strongly associated with hair loss. Consistent with this observation, hair growth is a reported side effect of administration of T4. Furthermore, T3 and T4 have been the subject of several patent publications relating to treatment of hair loss, including, for example, International Patent Application Publication No. WO 00/72810, published 7 Dec. 2000; International Patent Application Publication No. WO 00/72811, published 7 Dec. 2000; International Patent Application Publication No. WO 00/72812, published 7 Dec. 2000; International Patent Application Publication No. WO 00/72813, published 7 Dec. 2000; International Patent Application Publication No. WO 00/72920, published 7 Dec. 2000; and International Patent Application Publication No. WO 00/73292, published 7 Dec. 2000; and references cited therein.